Effect of indole‐3‐acetic acid (IAA) and sucrose on vessel size and density in isolated stem segments of oak (<i>Quercus robur</i>)

Abstract

The effects of several concentrations of indole‐3‐acetic acid (IAA) and sucrose on xylogenic cambial activity and secondary xylem differentiation were investigated in isolated stem segments of Quercus robur L. supplied with liquid medium in aseptic conditions. After 5 weeks of culture auxin controlled cambial cell division and the number and size of vessel elements even without sugar in the medium. Sucrose modified these IAA effects, although little cambial activity occurred without auxin. The xylem increment correlated with changes of auxin concentration with the optimum at 28.5 μ M IAA. The formation of wide vessels was correlated with the optimal concentration of auxin. The frequency of vessel differentiation increased with auxin concentration. High concentrations of sucrose (0.24 M and 0.96 M ) reduced both the number of vessels and their diameter. The frequency of vessel formation was inhibited more than the vessel size by changes of sugar concentration. The vessels formed under low concentrations of IAA were circular in transverse section. With increase in IAA concentration the shape of the vessel cross‐section changed to oval with the largest dimension in the radial direction.